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MXS-2359 Route statements with database but no table dependence

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Queries such as SHOW TABLES FROM db1 are now routed to the backend with db1.
This gives the correct result as long as db1 is not sharded to multiple
backends.
This commit is contained in:
Esa Korhonen 2019-03-26 14:19:57 +02:00
parent ee88180c54
commit c4b82b7d83
2 changed files with 43 additions and 21 deletions
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8
Documentation/Routers/SchemaRouter.md
View File

@ -233,8 +233,12 @@ answers correctly to the basic version of the query. Any modifiers such as `LIKE
ignored.
* `SHOW TABLES` is routed to the server with the current database. If using table-level
sharding, the results will be incomplete. Use `SHOW SHARDS` to get results from the router
itself.
sharding, the results will be incomplete. Similarly, `SHOW TABLES FROM db1` is routed to
the server with database `db1`, ignoring table sharding. Use `SHOW SHARDS` to get results
from the router itself.
* `USE db1` is routed to the server with `db1`. If the database is divided to multiple
servers, only one server will get the command.
## Examples

56
server/modules/routing/schemarouter/schemaroutersession.cc
View File

@ -1630,41 +1630,59 @@ SERVER* SchemaRouterSession::get_query_target(GWBUF* buffer)
int n_databases = 0;
char** databases = qc_get_database_names(buffer, &n_databases);
for (int i = 0; i < n_databases; i++)
if (n_databases > 0)
{
for (int j = 0; j < n_tables; j++)
// Prefer to select the route target by table. If no tables, route by database.
if (n_tables)
{
SERVER* target = m_shard.get_location(tables[j]);
if (target)
for (int i = 0; i < n_tables; i++)
{
if (rval && target != rval)
SERVER* target = m_shard.get_location(tables[i]);
if (target)
{
MXS_ERROR("Query targets tables on servers '%s' and '%s'. "
"Cross server queries are not supported.",
rval->name,
target->name);
}
else if (rval == NULL)
{
rval = target;
MXS_INFO("Query targets table '%s' on server '%s'",
tables[j],
rval->name);
if (rval && target != rval)
{
MXS_ERROR("Query targets tables on servers '%s' and '%s'. "
"Cross server queries are not supported.",
rval->name, target->name);
}
else if (rval == NULL)
{
rval = target;
MXS_INFO("Query targets table '%s' on server '%s'", tables[i], rval->name);
}
}
}
}
else if (rval == nullptr)
{
// Queries which target a database but no tables can have multiple targets. Select first one.
for (int i = 0; i < n_databases; i++)
{
SERVER* target = m_shard.get_location(databases[i]);
if (target)
{
rval = target;
break;
}
}
}
}
// Free the databases and tables arrays.
for (int i = 0; i < n_databases; i++)
{
MXS_FREE(databases[i]);
}
MXS_FREE(databases);
for (int i = 0; i < n_tables; i++)
{
MXS_FREE(tables[i]);
}
MXS_FREE(tables);
MXS_FREE(databases);
return rval;
}